Sensorless Haptic Control for Physical Human–Robot Interaction

Industrial robots can offer fast speed and high accuracy for task execution but are far behind humans in terms of flexibility, adaptability, controllability, and even predictability. Therefore, combining the strength, accuracy, and speed of robots with flexibility, adaptability and controllability can achieve high-quality performance in human–robot interaction. In addition, humans in the manufacturing sector often need to adapt to the pre-planned/pre-defined tasks, dynamically. However, the robots used nowadays are controlled by pre-generated codes that cannot support effective human–robot interaction. Most industrial robots do not have built-in torque/force sensors in the joints and have difficulty in installing external force/torque sensors on the end-effectors. Additionally, the available signals from a robotic system are limited. To address such challenges, this chapter presents an approach to haptically controlling an industrial robot without using any external sensors for effortless and natural human–robot interaction. This sensorless haptic control approach is enabled by the dynamic models of the robot where only joint angles and joint torques are measurable. To have better interaction performance, accurate modelling of the dynamic model of the robot both in the presliding and sliding regimes is developed to estimate the joint torques where the friction model is thoroughly explored. The estimated external force applied to the robot by an operator is transferred into reference position and speed of the robot by an admittance controller, and adaptive admittance parameters are adopted to make human–robot interaction more natural and easier with accurate positioning and control and smooth movement. Finally, the proposed approach is validated by a case study in which a human operator interacts with an industrial robot.